
---> go to "C:\Program Files (x86)\Rockstar Games\Grand Theft Auto IV\pc\audio\Sfx", and save the file "resident.rpf".

1/ Download sparkIV (v1.0.7.0) : http://www.gtainside.com/en/download.php?cat=326&do=comments&id=28310
2/ Open Spark IV. Click on "GTAIV" on the top of the left corner.
3/ In the left part of the window, find a folder called "sfx" (in "gtaIV/pc/audio") and click on.
4/ In the right part of the window, find a file called "resident". Double click on it.
5/ A new window appears. In the left part, click on "RESIDENT" and in the right part, one click on "RAIN.ivaud".
6/ On the top of the main window, click on "import", select the "RAIN.ivaud" of my mod, and confirm.
---> Click on "Save", and the rain sounds are now deleted...

Enjoy !!